PCI: Document hybrid devres hazards

These functions:

  pci_request_region()
  pci_request_regions()
  pci_request_regions_exclusive()
  pci_request_selected_regions()
  pci_request_selected_regions_exclusive()
  pci_intx()

are "hybrid" functions that are managed if pcim_enable_device() has been
called, but unmanaged otherwise.

This is confusing and has already caused a bug (in 8558de401b5f
("drm/vboxvideo: use managed pci functions")) because users believe all PCI
functions, such as pci_iomap_range(), can become managed that way, which is
not the case.

Add comments to the relevant functions' docstrings that warn users about
this behavior.

Link: https://lore.kernel.org/r/20240613115032.29098-7-pstanner@redhat.com
Signed-off-by: Philipp Stanner <pstanner@redhat.com>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
[bhelgaas: commit log]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

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